Sudoku Generator - Create Printable Sudoku Puzzles

How to use this tool

1. Choose a difficulty level.
2. Click "New Puzzle" to generate a fresh board.
3. Click a cell and type a digit 1–9. Use Backspace to clear.
4. Click "Check" to highlight mistakes, or "Solve" to reveal the solution.

Sudoku rules

Sudoku is a 9×9 number puzzle divided into nine 3×3 boxes. Fill every cell with a digit from 1 to 9 so that each row, each column, and each 3×3 box contains every digit exactly once. The puzzle starts with some cells already filled (called “givens”); your task is to deduce the remaining digits using logic alone - no guessing is needed for a well-formed puzzle.

Difficulty levels and givens

These are approximate starting clue counts observed from this generator. Expert puzzles may retain extra clues when the uniqueness check prevents further removals. The listed techniques are examples commonly associated with puzzles at this density; the generator does not grade by human techniques. Each difficulty sets a clue-removal target, and a removal is kept only when the puzzle remains uniquely solvable.

Core solving strategies

• Naked single: a cell has only one digit that can legally go there. This is the simplest technique and fills most cells in easy puzzles.
• Hidden single: within a row, column, or box, one digit has only one possible cell - even if that cell still has multiple candidates.
• Naked pair: two cells in the same unit share exactly the same two candidates. Those two digits can be eliminated from all other cells in that unit.
• Pointing pair/triple: if a digit’s candidates in a box all fall within the same row or column, that digit can be eliminated from the rest of that row or column outside the box.
• X-wing: if a digit appears in exactly two cells in each of two rows, and those cells share the same two columns, then that digit can be eliminated from the rest of those columns.

Solving strategy progression

Techniques in order of increasing difficulty - work through them in sequence when you get stuck:

1. Naked singles: only one digit fits in the cell.
2. Hidden singles: only one cell in a unit can hold a particular digit.
3. Naked pairs/triples: two/three cells share the same two/three candidates.
4. Pointing pairs: candidates in a box confined to one row or column.
5. X-wing: a digit locked to two rows and two columns simultaneously.
6. Swordfish: like X-wing but spanning three rows and three columns.
7. Forcing chains / bifurcation: last resort - assume a candidate and follow consequences.

How the puzzle is generated

The generator starts by filling a complete valid 9×9 grid (which can be done quickly by solving an empty board with the backtracking algorithm). It then considers cell positions in randomized order and tries removing their clues one at a time. A removal is kept only when a solution count confirms the puzzle still has exactly one valid solution; otherwise the clue is restored. Each difficulty targets a number of clues to remove, rather than a target number of givens to keep. The generator stops when it reaches that removal target or has checked all positions, so Expert may retain extra clues if uniqueness prevents more removals. Difficulty tiers use removal targets and uniqueness checks, not human-technique grading.

Daily puzzle challenge

Many sudoku enthusiasts treat the puzzle as a daily mental exercise. Consider printing one Expert-level puzzle per week as a focused challenge - solving on paper without hints builds stronger pattern recognition than solving digitally. Newspaper sudoku puzzles are graded by day of the week, with Monday being easiest and Saturday the hardest.